gallium/util: set right dst-dimensions

This should have been the destination surface size, not the dimensions
of the source box. These were the same in the test-case I used while
developing this, but this matters for the GTF framebuffer-blit
functional CTS tests.

Fixes: e8a40715a8b ("gallium/util: add blitter-support for stencil-fallback")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6898>
diff --git a/src/gallium/auxiliary/util/u_blitter.c b/src/gallium/auxiliary/util/u_blitter.c
index e21076c..cb810af 100644
--- a/src/gallium/auxiliary/util/u_blitter.c
+++ b/src/gallium/auxiliary/util/u_blitter.c
@@ -2859,7 +2859,7 @@
 
    blitter_set_common_draw_rect_state(ctx, false,
       util_framebuffer_get_num_samples(&fb_state) > 1);
-   blitter_set_dst_dimensions(ctx, srcbox->width, srcbox->height);
+   blitter_set_dst_dimensions(ctx, dst_view->width, dst_view->height);
 
    pipe->clear_depth_stencil(pipe, dst_view, PIPE_CLEAR_STENCIL, 0.0, 0,
                              dstx, dsty, srcbox->width, srcbox->height,